Blue-emitting Phosphor Research Articles

Eu2+-doped Sr5(PO4)3Br blue-emitting phosphor with high color purity for near-UV-pumped white light-emitting diodes

Eu2+-doped bromophosphateapatite Sr5(PO4)3Br phosphors were synthesized by the conventional high-temperature solid-state reaction. The crystal structure and luminescence properties of the phosphors, as well as their thermal stability and CIE chromaticity coordinates were systematically investigated. Photoluminescence spectra of Sr5(PO4)3Br:Eu2+ exhibit a single blue emission at 450 nm under the excitation of 345 nm, which is ascribed to the 4f–5d transition of Eu2+. The phosphor shows very good thermal stability. The CIE color coordinates are very close to those of BaMgAl10O17:Eu2+ (BAM). All the properties indicate that the blue-emitting Sr5(PO4)3Br:Eu2+ phosphor has potential application in white LEDs.

High-efficiency and thermal-stable Ca3La(GaO)3(BO3)4:Eu3+ red phosphors excited by near-UV light for white LEDs

The Ca3La(GaO)3(BO3)4:Eu3+ (CLGB:Eu3+) red-emitting phosphors with high-efficiency and splendid thermal stability were prepared by a solid-state method. The synthesized samples were analyzed by X-ray diffraction, photoluminescence spectra, fluorescence decay curves, temperature-dependent photoluminescence spectra, diffuse reflection spectra and internal quantum efficiency. All the CLGB:Eu3+ compounds showed strong red emission peaking at around 621 nm under 397 nm excitation and the best doping concentration was 60 mol%. What's more, CLGB:Eu3+ phosphors also displayed excellent thermal stability and the emission intensity at 423 K maintained 78.6% of original value at 303 K. Furthermore, the internal quantum efficiency of the resultant phosphors reached up to 82.2%. By combining a near-ultraviolet chip, (Ba,Sr)2SiO4:Eu2+ green-emitting phosphors, BaMgAl10O17:Eu2+ blue-emitting phosphors and CLGB:0.6Eu3+ red-emitting phosphors, the fabricated light-emitting diode can generate bright white light with low correlated colour temperature of 3964 K and high colour rendering index of 85. All of these achieved results demonstrate that the CLGB:Eu3+ compounds are potential red-emitting phosphors for the near-ultraviolet chip excited white light-emitting diodes.

Exploring Defect-Induced Emission in ZnAl2O4: An Exceptional Color-Tunable Phosphor Material with Diverse Lifetimes.

Activator-free zinc aluminate (ZA) nanophosphor was synthesized through a sol-gel combustion route, which can be used both as a blue-emitting phosphor material and a white-emitting phosphor material, depending on the annealing temperature during synthesis. The material also has the potential to be used in optical thermometry. These fascinating color-tunable emission characteristics can be linked with the various defect centers present inside the matrix and their changes upon thermal annealing. Various defect centers, such as anionic vacancy, cationic vacancy, antisite defect, etc., create different electronic states inside the band gap, which are responsible for the multicolor emission. The color components are isolated from the complex emission spectra using time-resolved emission spectroscopy (TRES) study. Interestingly, the lifetime values of the various defect centers were found to change significantly from milliseconds to microseconds upon thermal annealing, which makes the phosphors more diverse (i.e., either long-persistent blue-emitting phosphors or short-persistent white-emitting phosphors). Fourier transform infrared (FTIR) and diffuse reflectance spectroscopy (DRS) confirmed the presence of antisite defect centers such as AlZn+ or ZnAl- in the matrix. X-ray absorption fine structure (EXAFS) study showed that the spinel structure was more disordered in nature for low-temperature-annealed compounds. Electron paramagnetic resonance (EPR) and positron annihilation lifetime spectroscopy (PALS) studies were also carried out in order to characterize various anionic and cationic vacancies and their clusters present in the compounds. Antisite defect centers such as AlZn+ or ZnAl-, which act as an electron or hole trap, were found to be responsible for the diverse lifetime behavior. To gain insight about the electronic states inside the band gap, density functional theory (DFT)-based calculations were performed for both pure and various vacancy-introduced spinel structures. Finally, based on the theoretical and experimental results, for the first time, a detailed investigation of various defect-induced emission behavior in ZA is presented, which also explains the mechanism of color tunability and dynamic lifetimes.

High-brightness and high-color purity red-emitting Ca3Lu(AlO)3(BO3)4:Eu3+ phosphors with internal quantum efficiency close to unity for near-ultraviolet-based white-light-emitting diodes.

In this work, we reported on high-brightness Eu3+-activated Ca3Lu(AlO)3(BO3)4 (CLAB) red-emitting phosphors. Under 397nm excitation, the CLAB:Eu3+ phosphors showed intense red emissions at around 621nm with CIE coordinates of (0.657, 0.343). The optimal doping concentration of Eu3+ ions was found to be 30mol. %, and the CLAB:0.3Eu3+ sample possessed high-color purity of 93% and ultra-high internal quantum efficiency as great as 98.5%. Importantly, the CLAB:0.3Eu3+ also had good thermal stability. Finally, a white-light-emitting diode (WLED) lamp with good color-rendering index was fabricated by using a 365nm ultraviolet chip and the phosphor blends of CLAB:0.3Eu3+ red-emitting phosphors, (Ba,Sr)2SiO4:Eu2+ green-emitting phosphors, and BaMgAl10O7:Eu2+ blue-emitting phosphors.

Electron-vibrational interaction in the 3d states of Cu+ ions activated in Na5Ca4(PO4)4F

Cu+-doped Na5Ca4(PO4)4F fluorophosphate was synthesized by wet-chemical method. This blue-emitting phosphor was characterized by XRD, FTIR and photoluminescence measurements. Rietveld refinement method was employed to analyse the phase formation of the as-prepared phosphor. The electron-vibrational interaction (EVI) parameters were calculated by the spectrum-fitting method. Na2Ca4(PO4)3F:Cu+ phosphor demonstrated blue emission under near-UV excitation and its CIE coordinates were found at (0.151, 0.037).

Synthesis, luminescence and application of BaKYSi2O7:Eu2+: A new blue-emitting phosphor for near-UV white-light LED

A series of new silicate phosphors, Ba1-xEuxKYSi2O7 (BKY: Eu2+) (x = 0.005, 0.01, 0.02, 0.05, 0.07) have been synthesized from a water-soluble propylene glycol modified silane (PGMS) based silicon precursor by a solution approach. This phosphor can be efficiently excited by near-UV light and generates a broadband bright blue emission with internal Quantum Efficiency 34%. The detailed crystal structure of monoclinic BKY:Eu2+ was determined from the XRD profile using Rietveld refinement. Band gap was determined from Diffuse Reflectance Spectra using Kubelka Munk function. Steady state and time resolved Photoluminescence measurement as well as the thermal quenching properties of the phosphor have been investigated in detail. A highly efficient broadband blue emission centered at λmax ~ 460 nm with a full-width at half-maximum of 72 nm shows very low thermal quenching; 83.2% at 150 °C with respect to that measured at room temperature. Moreover, a white LED device has been fabricated by coating the as-synthesized phosphor with a standard red emitting CaAlSiN3:Eu2+ phosphor and a standard green emitting Ba2SiO4:Eu2+ phosphor. The LED device exhibited an excellent color-rendering index CRI of 84.0564 at a correlated color temperature of 3752.4 K with CIE color coordinates of (0.363, 0.293) under a 350 mA forward-bias current. The interesting excitation profile and robust thermal performance reflect the potential application of this phosphor for near UV- LED driven solid state lighting.

Development of a potential blue-emitting phosphor Ba3BPO7:Tm3+, Na+ excited by near-ultraviolet

The present work developed a potential blue-emitting phosphor Ba3BPO7:Tm3+, Na+ excited by near-ultraviolet (UV), which was prepared via conventional high-temperature solid-state reaction. The structural and morphological properties of the as-prepared phosphors were evaluated by the powder X-ray diffraction and scanning electron microscopy, respectively. The luminescence properties of Tm3+ in Ba3BPO7 host including photoluminescence excitation and emission spectra, decay curves, and chromaticity coordinates were investigated in detail. Under near-UV (357 nm) excitation, the as-prepared phosphor shows sharp emission peak at 452 nm due to the 1D2 → 3F4 transition of Tm3+, leading to satisfactory blue emission with short decay lifetime (microsecond-level) and high color purity. Furthermore, the critical distance and concentration quenching mechanism were also investigated based on the concentration quenching phenomenon of Tm3+ in Ba3BPO7 host. The obtained results indicate Ba3BPO7:Tm3+, Na+ phosphor could have potential application in the area of solid state lighting based on the near-UV w-LEDs.

A novel Sm3+ singly doped LiCa3ZnV3O12 phosphor: a potential luminescent material for multifunctional applications.

The Sm3+ ion singly doped LiCa3ZnV3O12 (LCZV) phosphors were synthesized by a traditional high-temperature solid-state method. The luminescence characteristics of the as-prepared samples were studied by photoluminescence excitation and emission spectra. Under 343 nm excitation, the synthesized phosphors exhibited color controllable emission induced by the efficient energy transfer from VO43− groups to Sm3+ ions. Besides, the energy transfer efficiency was revealed to be about 58.4% when the dopant concentration was 4 mol%. By utilizing the as-prepared LCZV:Sm3+ phosphors, commercial BaMgAl10O7:Eu2+ blue-emitting phosphors and a near-ultraviolet light-emitting diode (LED) chip, a white LED device was fabricated. Under an injection current of 100 mA, the packaged LED device emitted pure white light with high color rendering index (88.4) and proper correlated color temperature (4320 K). By analyzing the thermal quenching behavior of the VO43− groups and Sm3+ ions, the optical thermometric behavior of the Sm3+-doped LCZV compounds was investigated. The maximum absolute sensor sensitivity and relative sensor sensitivity were found to be 0.25 K−1 and 1.8% K−1, respectively. Additionally, the emitting color of the studied samples was dependent on the temperature. Ultimately, the Sm3+-doped LCZV phosphors were potential candidates for indoor illumination, optical thermometry and safety signals in high temperature environments.

Density functional theory investigation on iridium(iii) complexes for efficient blue electrophosphorescence.

The geometrical structures, electronic structures, optoelectronic properties and phosphorescence efficiencies of four blue-emitting phosphors [Ir(fpmi)2(pyim)] (1), [Ir(pyim)2(fpmi)] (2), [Ir(fpmi)2(fptz)] (3), [Ir(tfmppz)2(pyim)] (4), [fpmi = 1-(4-fluorophenyl)-3-methylimdazolin-2-ylidene-C,C2′; pyim = 2-(1H-imidazol-2-yl)pyridinato; fptz = 5-(trifluoromethyl-2H-1,2,4-triazol-3-yl)pyridine; tfmppz = 1-(4-trifluoromethylphenyl)pyrazolyl] were investigated by DFT and TDDFT methods. We first optimized geometrical structures in the ground and lowest triplet states, and computed the absorption and emission spectra of 1 and 5[Ir(fpmi)2(pypz)] [pypz = 2-(1H-pyrazol-5-yl)pyridinato], which have been synthesized and characterized in a laboratory, using three functionals, B3LYP, CAM-B3LYP, and M062X. The calculation results were compared with relevant experimental data to assess the performance of the functionals. The suitable methods and functionals were then applied to study properties of the three other complexes. The HOMOs of 1–3 are composed of d(Ir) and π(cyclometalated ligands), however, the HOMO of 4 resides on the pyim ligand, while the LUMOs of all four complexes are dominantly localized on the chelating ligands. The calculated absorption results show that the corresponding absorption peaks for the four mainly studied complexes are almost at the same positions, however, the absorption intensities of the bands differ largely from each other. The lowest energy emissions of the four complexes are localized at 507, 512, 468, and 513 nm, respectively. In order to estimate their efficiencies, we carried out simplified radiative rate constant calculations. It turns out that complex 3, which possesses the shortest emission wavelength and the largest radiative rate constant (kr) value, can be considered as a highly efficient blue-emitting iridium(iii) complex.

Optical performance of the Ba5Al3F19:Eu2+ blue phosphors with high thermal stability

Ba5Al3F19:Eu2+ blue-emitting phosphors were synthesized by the solid state reaction in a reductive atmosphere. The crystal structure of Ba5Al3F19:Eu2+ phosphors were characterized by using the X-ray powder diffraction (XRD) measurement. The luminescence properties are investigated systematically based on the crystal structure. Emission and excitation spectra of the Ba5Al3F19:Eu2+ phosphor along with the decay curves were characterized. Under the excitation of UV light, the phosphor exhibits a broad band emission around 410 nm ascribed to the allowed 4f65d→4f7(8S7/2) transition, together with a sharp line at 360 nm corresponding to the forbidden 4f7(6P7/2)→4f7(8S7/2) transition of the Eu2+ ions. The temperature dependent emission spectra and decay curves were measured to investigate the origins of the emission and the thermal stabilities of the as-prepared phosphors. The as-prepared Ba5Al3F19:Eu2+ phosphors display interesting and stable luminescence properties, which can act as promising blue-emitting phosphor candidates.

Luminescence properties of Eu2+-activated NaCaBeSi2O6F for white light-emitting diode applications

A series of blue-emitting NaCaBeSi2O6F:Eu2+ phosphors were obtained via a solid state reaction. NaCaBeSi2O6F:Eu2+ exhibit a broad absorption from 250 to 450nm when monitored at 467nm and display a broad emission band from 400 to 600nm when excited at 397nm. The concentration quenching was obtained when the concentration of Eu2+ was increased to 0.8mol%. Energy transfer interactions between Eu2+ in host is due to dipole-dipole mechanisms and the critical distance was calculated to be 31.96Å. The results obtained in this study highly indicates that NaCaBeSi2O6F:Eu2+ can be a potential blue-emitting phosphor for light quality improvement in white-LED applications.

Synthesis and luminescence properties of Ca5-x(PO4)3Br: xEu2+—A novel blue-emitting bromapatite phosphor for near-ultraviolet-pumped white light-emitting diodes

A series of novel Ca5-x(PO4)3Br: xEu2+ (x=0.01–0.10) blue phosphors were synthesized via the conventional solid state reaction and their luminescence properties were reported. The Ca5-x(PO4)3Br: xEu2+ phosphors could be excited efficiently in the wavelength range of 320–440nm and displayed an intense asymmetric blue emission band around 458nm under 365nm excitation. The concentration quenching of Eu2+ in the Ca5(PO4)3Br host was investigated in detail. The optimum doping concentration of Eu2+ was determined to be 0.07 and the energy transfer mechanism was certified to be the dipole–dipole interaction. Moreover, the CIE chromaticity coordinates for the composition-optimized Ca4.93(PO4)3Br: 0.07Eu2+ were located in the blue region at (x=0.1450, y=0.0840), whose color purity was close to that of the commercial blue phosphor BaMgAl10O17: Eu2+. All these results gave an indication that Ca5-x(PO4)3Br: xEu2+ phosphors could serve as a promising blue-emitting candidate for near-UV-pumped white light-emitting diodes.

New phosphors based on the reduction of Eu(III) to Eu(II) in ion-exchanged aluminosilicate and gallium silicate inorganic polymers

Novel blue-emitting phosphors based on Eu2+ ions dispersed within chemosynthetic aluminosilicate and gallium silicate inorganic polymer (geopolymer) hosts were prepared by heat treatment of Eu3+-exchanged inorganic polymers in reducing conditions and investigated using photoluminescence spectroscopy, 29Si, 27Al and 71Ga MAS NMR spectroscopy, XRD, and XPS. Eu2+ photoluminescence could be distinguished from the photoluminescence of the inorganic polymer host after heating at ≥ 400°C in the case of the aluminosilicate inorganic polymer and ≥ 600°C in the case of the gallium silicate inorganic polymer and became more intense as the reduction temperature was increased up to 1000°C. The gallium silicate-based phosphors heated at ≥ 900°C contained small amounts of crystalline KGaSi2O6 or β-Ga2O3, but the X-ray amorphous structure of the inorganic polymer was retained. After heating at 1000°C, the Eu2+ photoluminescence intensity was substantially more intense for the aluminosilicate phosphor, but the shape of the excitation and emission spectra of the aluminosilicate and gallium silicate phosphors were similar, with a broad emission band centred at 440–475nm when excited at 240–400nm. This band shifted to longer wavelengths as the ion exchange solution concentration was increased from 0.001M to 0.03M.

Eu3+-activated La2MoO6-La2WO6 red-emitting phosphors with ultrabroad excitation band for white light-emitting diodes

A series of novel Eu3+-activated La2MoO6-La2WO6 red-emitting phosphors have been successfully prepared by a citrate-assisted sol-gel process. Both photoluminescence excitation and emission spectra suggest that the resultant products have the strong ultrabroad absorption band ranging from 220 to 450 nm. Under the excitation of 379 nm, the characteristic emissions of Eu3+ ions corresponding to the 5D0 → 7FJ transitions are observed in the doped samples. The optimal doping concentration for Eu3+ ions is found to be 12 mol% and the quenching mechanism is attributed to the dipole-dipole interaction. A theoretical calculation based on the Judd-Ofelt theory is carried out to explore the local structure environment around the Eu3+ ions. The studied samples exhibit a typical thermal quenching effect with a T0.5 value of 338 K and the activation energy is determined to be 0.427 eV. A near-ultraviolet (NUV)-based white light-emitting diode (LED) is packaged by integrating a mixture of resultant phosphors, commercial blue-emitting and green-emitting phosphors into an NUV LED chip. The fabricated LED device emits glaring white light with high color rendering index (84.6) and proper correlated color temperature (6492 K). These results demonstrate that the Eu3+-activated La2MoO6-La2WO6 compounds are a promising candidate for indoor lighting as red-emitting phosphors.

Mid-term (5–10 year) results of the Salto Talaris total ankle arthroplasty

A novel high thermal stability Ca5(SiO4)2F2:Ce3+,Na+ blue-emitting phosphor was synthesized by solid-state reaction. The excitation spectrum shows a broad band extending from 200 nm to 390 nm, and the emission spectrum shows a broad blue band peaking at 408 nm with a half width of approximately 75 nm. The optimum doping concentration of Ce3+ is found to be 8 mol%. Its luminescence intensity at 420 K still kept by approximately 86% of the initial value at room temperature. The calculated CIE coordinates indicate that the phosphor has good color purity. Given their broadband absorption from 250 nm to 390 nm, these phosphors meet the application requirements for GaN-based light-emitting diodes.

Crystal structure and luminescence properties of a novel non-rare-earth activated blue-emitting garnet phosphor Ca4ZrGe3O12: Bi3+ for n-UV pumped light-emitting diodes

A novel Bi3+ activated Ca4ZrGe3O12 phosphor was synthesized and the photoluminescence properties were investigated. Ca4ZrGe3O12:Bi3+ could be efficiently excited in the wavelength range of 320–430 nm, and exhibit a broad emission band (400–520 nm) with a peak at 435 nm corresponding to the 3P1–1S0 transition of Bi3+. Due to the energy transfer between Bi3+ ions, the concentration quenching in the Ca4ZrGe3O12 host occurred when the concentration of Bi3+ exceeded 2.25 mol %. Upon excitation at 370 nm, the internal quantum efficiency of the phosphor with different Bi3+ concentration was measured, the highest value was determined to be 38.6%. Moreover, the phosphor exhibited excellent thermal stability and the corresponding activation energy ΔE was determined to be 0.228 eV. Due to the efficient excitation in the near ultraviolet (n-UV) region and the strong blue emission, Ca4ZrGe3O12:Bi3+ would be a potential blue phosphor for n-UV pumped light-emitting diodes.

Eu2+-doped Ba2GaB4O9Cl blue-emitting phosphor with high color purity for near-UV-pumped white light-emitting diodes

Eu2+-doped borate fluoride Ba2GaB4O9Cl was synthesized by the conventional high-temperature solid-state reaction. The crystal structure and luminescence properties of the phosphors, as well as their thermal luminescence quenching capabilities and CIE chromaticity coordinates were systematically investigated. Under the excitation at 340nm, the phosphor exhibited an asymmetric broad-band blue emission with a peak at 445nm, which is ascribed to the 4f–5d transition of Eu2+. It was further proved that energy transfer among the nearest neighbor ions is the major mechanism for concentration quenching of Eu2+ in Ba2−xGaB4O9Cl:xEu2+ phosphors. The luminescence quenching temperature is 432K. The CIE color coordinates are very close to those of BaMgAl10O17:Eu2+ (BAM). All the properties indicated that the blue-emitting Ba2GaB4O9Cl:Eu2+ phosphor has potential application in white LEDs.

A Blue-Emitting Phosphor of Tm3+ Ion-Doped BaY2ZnO5

A phosphor of Tm3+ ion-doped BaY2ZnO5 which exhibits an emission in the blue region is synthesized via a vibrating milled solid-state reaction with metal oxides. The x-ray powder diffractometry patterns show that all the diffraction peaks are attributed to the orthorhombic BaY2ZnO5 structure for the Tm3+ ion concentration doping from 1 mol.% to 7 mol.%. Upon excitation at a wavelength of 362 nm, the emission intensity of the 1D2 → 3F4 transition is at a maximum when the Tm3+ concentration is 2 mol.% and decreases as the Tm3+ concentration increases, and there is concentration quenching when x > 0.02. A single exponential decay is observed for diluted samples, and a non-exponential decay occurs when BaY2ZnO5 is doped with a greater concentration of the Tm3+ ion. The Tm3+ ion-doped BaY2ZnO5 phosphor exhibits a vivid blue emission with a wavelength of 458 nm which has the Commission Internationale de I’Edairage (CIE) color coordinates of x = 0.148 and y = 0.035, and color purity is more than 96%, which is superior to the reported purity for commercial blue phosphors, such as Y2O3:Tm and ZnS:Ag.

Self-activated multicolor emissions in Ca2NaZn2(VO4)3:Eu3+ phosphors for simultaneous warm white light-emitting diodes and safety sign

Self-activated Eu3+-doped Ca2NaZn2(VO4)3 multicolor-emitting phosphors were prepared by a facile critic-assisted sol-gel technique. Both the photoluminescence (PL) excitation and three-dimensional PL emission spectra revealed that the synthesized samples exhibited an intense absorption band in the range of 250–370 nm. The emission intensity of the phosphors was greatly dependent on the doping concentration and the optimal value was found to be 7 mol%. The concentration quenching mechanism is attributed to the dipole-dipole interaction and the critical distance is 18.8 Å. With the addition of Eu3+ ions, multicolor emissions were observed in the resultant phosphors when excited at 290 nm. The thermal stability of phosphors was characterized by temperature-dependent PL emission spectra. By manipulating the temperature, the emitting color of the prepared phosphors was tuned from yellowish red to orange, and ultimately to pure red. Additionally, the near-ultraviolet (NUV) chip-based light-emitting diode device, which was fabricated by coating the blended resultant phosphors, commercial blue-emitting and green-emitting phosphors on the NUV chip, emitted glaring warm white light with superior color rendering index and impressive correlated color temperature. These results suggest that the self-activated Eu3+-doped Ca2NaZn2(VO4)3 multicolor-emitting phosphors are suitable for safety sign in high temperature circumstance and indoor lighting.

Comprehension of the Effect of a Hydroxyl Group in Ancillary Ligand on Phosphorescent Property for Heteroleptic Ir(III) Complexes: A Computational Study Using Quantitative Prediction.

A new Ir(III) complex (dfpypya)2Ir(pic-OH) (2) is theoretically designed by introduction of a simple hydroxyl group into the ancillary ligand on the basis of (dfpypya)2Ir(pic) (1) with the aim to get the high-efficiency and stable blue-emitting phosphors, where dfpypya is 3-methyl-6-(2',4'-difluoro-pyridinato)pyridazine, pic is picolinate, and pic-OH is 3-hydroxypicolinic acid. The other configuration (dfpypya)2Ir(pic-OH)' (3) is also investigated to compare with 2. The difference between 2 and 3 is whether the intramolecular hydrogen bond is formed in the (dfpypya)2Ir(pic-OH). The quantum yield is determined by three different methods including the semiquantitative and quantitative methods. To quantitatively determine the quantum yield is still not an easy task to be completed. This work would provide some useful advices to select the suitable method to reliably evaluate the quantum yield. Complex 2 has larger quantum yield and more stability as compared with 1 and 3. The formation of intramolecular hydrogen bond would become a new method to design new phosphor with the desired properties.